We will investigate DNA transactions that involve multiple DNA- protein interactions and complex DNA topology. The direct visualization provided by electron microscopy is the method of choice for the study of these transactions because DNA folding, winding, or unwinding can be followed and DNA topology examined directly. Therefore, we are requesting a new transmission electron microscope that will provide special features and vastly enhanced availability. Topics for study include: site-specific recombination by phage lambda and Tn3 resolvase; DNA replication by phages lambda and P4 and by BPV and SV40 viruses; enhancer-mediated initiation of transcription by BPV. These processes involve multiple DNA-protein associations and long range DNA interactions. Our analysis should lead to a substantial advance in our understanding of those specific systems and the general nature of such complex DNA transactions.